Issues surrounding the diagnosis of perilymph fistula (PLF) present many challenges to the otologist. Since definitive criteria for the preoperative diagnosis and intraoperative confirmation of PLF have not been established, case definition criteria are uncertain. Prior clinical studies raise the suggestion that PLF may be more common than previously appreciated, but are characterized by a lack of prospective design and appropriate control groups. Phase I of this study proposes to utilize the unique constituency of perilymph proteins to develop a clinically applicable marker that is specific for the intraoperative diagnosis of PLF, and sensitive enough to detect perilymph in quantities as low as 2-5 microliters despite contamination by other adventitious fluids. Phase II clinical trials are also proposed: 1) assuming that a sensitive marker for PLF is developed, a multi- institutional prospective observational study is anticipated to study the prevalence of verifiable PLF and identify diagnostic prediction criteria in patients with auditory and vestibular dysfunction. 2) to address uncertainties regarding potential false negative results from intermittent PLF and microfistulae, a prospective randomized clinical trial involving patients with vestibular dysfunction is proposed to compare the efficacy of surgical treatment for presumed PLF with a control group treated in vestibular rehabilitation therapy. The aim of the research proposed is to understand the developmental mechanisms by which the cells of the retina achieve their specialized sub-types. glass mutations specifically remove the photoreceptor neurons of the Drosophila visual system; these cells begin to develop as neurons but fail to express photoreceptor specific genes, and later die. glass encodes a protein with five Zinc-finger domains; such proteins have been showm in other organisms to act as transcription factors. Thus glass may act directly to regulate photoreceptor cell-specific gene expression. We have shown that the glass protein binds in-vitro to sequences from enhancer elements of one such gene (a rhodopsin). glass is expressed in all the cells of the developing retina, but it is only active in the developing photoreceptors (by showing the affect on a reporter gene of glass DNA binding sites). Thus the regulation of glass activity is critical for photoreceptor cell development and this occurs at two levels: at transcription, and after translation (by incoming positional signals). To pursue this dual regulation we will conduct two projects: 1) To understand glass transcriptional regulation we will undertake a functional analysis of the glass gene promoter by mutational studies. 2) To identify novel genes that interact with glass we will use a series of genetic screens and the first will be for dominant enhancers and suppressors of weak glass areles. Preliminary screens have successfully tested the feasibility of this approach (we have recovered three such mutations). Once isolated we will characterize the effects of our novel mutations and in the long term, clone the genes responsible to study their molecular functions.